(a) Field of the Invention
This invention generally relates to an audio or musical amplifier. More particularly, but not by way of limitation, to an amplifier that uses vacuum tubes to control the output of transistors used in the processing of electrical signals that are to be used to drive audio equipment.
(b) Discussion of Known Art
The development of transistors allowed designers of musical or audio amplifiers to take advantage of the linear response characteristics of these devices in order to create musical, analog electrical signal amplification systems that exhibit very low distortion characteristics. These distortion characteristics are often used as parameters by which the fidelity or performance of a particular amplifier is measured. Therefore, using these parameters, transistor based devices, such as solid state amplifiers or even digital signal processing units that use transistor based amplifiers to drive speakers or the like, appear as being the logical optimal choice for sound reproduction. However, research has found that these rigidly linear amplification systems tend to amplify signals or sounds that are unpleasant to the ear with equal emphasis as the signals or sounds that are pleasing to the ear. Specifically, it is well accepted that the odd order harmonic distortion of a particular sound signal will be perceived as a harsh or un-musical sound by the human ear, whereas similar magnitude of distortion of even order harmonics is often perceived a coloring or enriching of the depth of the sound produced.
Still further, the load characteristics of an electromechanical device, such as a loudspeaker with coil activated components, produces complex electrical loading patterns that are difficult to model. Thus, the precise xe2x80x9cpsychoacousticxe2x80x9d behavior of a particular sound amplifier is often difficult to model in mathematical terms, but must be ascertained by actually listening to the system in operation. This aspect of evaluation of music or sound amplifiers is recognized in the article by Russell O. Hamm, titled Tubes Versus Transistors-Is There an Audible Difference? and published in the Journal of the Audio Engineering Society, May 1973, Volume 21, Number 4, pp.267-273, incorporated herein in its entirety by reference.
Known solid-state transistor designs offer advantages in that these devices provide high current delivery characteristics that allow solid state or transistor based amplifiers to drive speakers without the limitations of similar duty vacuum tube designs. Some the limitations of known vacuum tube designs include the large, lethal voltages required to produce a device that can supply enough current to drive loudspeakers and the like. Additionally, the large vacuum tubes and accompanying high voltage power supply required to bias or power the vacuum tubes that can drive large electromechanical devices, such as loudspeakers, can be prohibitively heavy and expensive.
Therefore, a review of known devices reveals that there remains a need for an amplifier that can provide the advantages of vacuum tube based designs and the current or power delivery advantages of transistor designs.
There remains a need for a sound amplifier that delivers the coloration and emphasis to sound as supplied by vacuum tube amplifiers while providing the power delivery characteristics, as well as the size, voltage, and weight characteristics of transistor based designs.
There remains a need for a device and method for multiplying the sonically desirable current transfer characteristics of vacuum tubes.
There remains a need for an amplifier design that allows reduction of manufacturing costs by utilizing conventional transistor design components that are controlled by vacuum tube components to create a system that exhibits vacuum tube performance.
There remains a need within an open loop or zero negative global feedback amplifier a variable system of increasing output transistor bias during crossover condition and alternately reducing output transistor bias during large signal operation in order to reduce total harmonic distortion (THD).
It has been discovered that the problems left unanswered by known art can be solved by providing an amplifier design that includes:
a vacuum tube;
a transistor, the transistor including a gate that controls the flow of current through the transistor, the vacuum tube being connected to the gate of the transistor, so that the current flow through the transistor is controlled by the vacuum tube. According to one example of the invention, the vacuum tube-transistor arrangement is set up in a xe2x80x9cpush-pullxe2x80x9d arrangement, where a vacuum tube-transistor combination controls positive voltages, and another vacuum tube-transistor combination controls the negative voltages delivered by the system, the system output being at approximately zero voltage when not under load.
It is also contemplated that signals to be amplified will be received by a vacuum tube, which will then react to this signal and control the flow of current through the transistor in response to this input signal. The input of the vacuum tube is wired such that the plate and the grid of the vacuum tube are connected to one another either directly or via a DC (Direct Current) component such as a resistor, diode or transistor and to the input signal. While this arrangement generally contemplates the use of vacuum tubes with a triode structure, other vacuum tube structures including the most simple diode type tubes may also be used. These other structures would also employ the primary control grid (if supplied) and additional grids or accompanying or enhancing structures by connections to the plate of the vacuum tube either directly or via common DC components.
Another important example of inventive concepts taught herein employs one of the most basic operating characteristics of vacuum tubes in a new and novel manner in order to significantly improve and enhance the operation of the invention. This vacuum tube characteristic was formerly called the xe2x80x9cEdison effectxe2x80x9d, disclosed in patents to Thomas A. Edison in 1883, but is now referred to as xe2x80x9cthermionic emission.xe2x80x9d
In a typical modern vacuum tube, thermionic emission occurs when the electron-emitting structure or cathode is heated. The heated cathode emits free electrons in close proximity and creates around itself what may be described as an xe2x80x9celectron cloud.xe2x80x9d The freely moving electrons within this electron cloud impinge themselves upon other structures within their immediate proximity, especially the plate. Thermionic emissions from the heated cathode have the measurable effect of increasing the potential voltage on the cathode as negatively charged electrons are emitted, and decreasing the potential voltage on other proximate electrodes and structures within the tube, especially the plate, which is purposefully designed as a very efficient receiver of such electrons.
According to another important aspect of the invention taught herein, illustrated herein as FIG. 2, which shows a novel method to utilize such thermionic emissions from vacuum tubes to variably regulate output transistor bias current resulting in substantially reduced THD. Specifically, this novel use of vacuum tube thermionic emissions is especially helpful during the wellknown and problematic conditions of signal xe2x80x9ccrossoverxe2x80x9d within typical A-B style, push-pull amplifiers and also during xe2x80x9clarge signal outputxe2x80x9d conditions.
Properly utilized within the invention, vacuum tube thermionic emission properties may provide the means to variably increase output transistor bias voltage and current during crossover periods and alternately decrease output transistor bias voltage and current during large signal operation. The overall result is typically an order of magnitude less THD. The new method of utilizing vacuum tube thermionic emissions taught herein to provide a means of variable bias voltage and current for the output transistors greatly enhances the invention and provides for an improved xe2x80x9copen loopxe2x80x9d or xe2x80x9czero negative global feedbackxe2x80x9d version of a vacuum tube hybrid audio amplifier.
According to yet another important invention taught herein, a vacuum tube with auxiliary illumination is also disclosed. This arrangement includes the structure commonly found in well-known vacuum tubes, being a base, connectors, and glass tube, and an illumination component. According to a method taught herein, the illumination component is positioned in close proximity to the glass tube of the vacuum tube. With this arrangement the illumination component servers to provide enhanced illumination to the vacuum tube, further-enhancing the colored illumination given off by many vacuum tubes during operation.
According to one example of the system using an illumination component, the illumination component is incorporated as a part of the base of the vacuum tube. Thus, it is contemplated that an illumination device, such as a light emitting diode (LED), is incorporated directly into the base of the vacuum tube. This arrangement allows the improved vacuum tube disclosed herein directly into a commercially available socket used to mount the vacuum tube onto the circuitry of the amplifier or other device. It is contemplated that the power to operate the LED, or other illumination component, would be drawn from one or more of the pins on the base of the vacuum tube. A voltage and/or current reducing element, for example a resistor, would be used to reduce the voltage drawn from the pins on the base.
As will be discussed further, below, it is contemplated that the LED, or other illumination component, may be positioned within the glass tube, or next to it on the base. An important new and useful result that is achievable with this arrangement is the indication of the fact that current is available to the tube that includes the disclosed illumination system. This solves a problem that is inherent in vacuum tubes, and that is that the vacuum tubes do not become operation the instant that power is delivered to the tube. The emitter of a vacuum tube must achieve the proper operating temperature before it becomes fully functional. Thus, the user would have to wait until the tubes warmed up before the user could determine whether the vacuum tube is connected to electrical power.
It is further contemplated that the illumination component would be of a type that emits light that approximates the color of the light naturally given off by a fully operational vacuum tube. Of course, it is also contemplated that the light-emitting device may be of any color and used to provide additional visual information to the user. For example, additional LEDs may be imbedded into the base of the vacuum tube and circuitry that is responsive to the voltage drop across selected terminals of the vacuum tube may then be incorporated to illuminate different colored or selected LEDs for a visual indicator of the operation or load being delivered through the vacuum tube, etc. Ideally, these LEDs would be positioned in an inconspicuous location, so that the overall appearance of the vacuum tube is not altered.
It should also be understood that while the above and other advantages and results of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings, showing the contemplated novel construction, combinations and elements as herein described, and more particularly defined by the appended claims, it should be clearly understood that changes in the precise embodiments of the herein disclosed invention are meant to be included within the scope of the claims, except insofar as they may be precluded by the prior art.